During operation, the HDDs generate create vibration as they rotate. By definition, a hard drive system will undergo rotational vibration when an oscillating moment is applied. When a hard disk drive is idle, the oscillation can be caused by friction in the spindle bearings or by rotational imbalance of the platter(s). When the drive is under read/write or seek conditions, inertia forces from activity of the actuator arm can cause rotational vibration (RV) is characterized by rad/s, which is the rotational analog of linear acceleration m/s2 or g. When HDDs are packaged in close proximity they can, and most often will, propagate RV from one drive to another degrading drive performance. The vibration can become excessive, particularly when adjacent HDDs are operated simultaneously. Moreover, as HDD technology progresses to faster rotational speeds and cost-reduction architectures, the vibration problems are exacerbated.
In addition to the drive-to-drive induced vibration, there is also the real possibility of vibration being induced by the environment in which the drives are located. As an example of this would be in a data closet, where network storage equipment is maintained, there could be a number of external sources that can induce vibration. An air conditioner in any relatively near location would be a specific example.
Vibration can also come in the form of acoustic vibration or the HDDs can produce disturbing acoustic noise, particularly for the consumer product applications. As personal computer become more prevalent in the home and HDDs are being used for audio/video and entertainment applications, acoustic noise emissions are becoming important to consumers. Another factor in determine performance is acoustic noise by the HDD. For example, research has found that the leading question by consumers with respect to hard drives was “How loud will this drive be in my system? The acoustic noise comes from two noise generally comes from two sources.
Excessive vibration may lead to decreased HDD performance such as recoverable and non-recoverable write inhibits, increased seek times, and increased read and write access times. Excessive vibration or shock may also cause premature HDD failures that are not repairable. Examples include mechanically-damaged platters and read/write heads, mechanical wear on moving HDD components, and data error defects that cannot be corrected through the use of software tools. Also many HDDs in a confined space results in a substantial amount of heat generation. This heat must be dissipated in order to avoid over heating the HDDs and causing shortened product life.
Currently, there is a void in the market as far as a complete solution that addresses vibration, thermal, and all other physical issues (mass, structure . . . ) for hard drives. The proliferation of hard drives is growing rapidly. The typical CAGR (compound annual growth rate) for the various segments of the Storage Area Network (SAN) and Network Attached Storage (NAS) arenas are growing at an .about.67% (typical). An increase in HDD performance will have a significant effect when considering the tremendous numbers of drives in operation.
Much of the HDD industry continues to ignore the threat of damaging vibration as failure rates become exceedingly high and grasp at ineffective solutions. The nature of almost all problems is the need to resolve opposing constraints. The constraints invariably pull any of the possible solutions to a problem in different directions. Almost without fail, all solutions find that in improving one problem constraint that they diminish the solution from the aspect of one, or more, of the other imposed constraints. The position of making trade-offs and finding a “balance” of the capabilities needed to satisfy the need(s). An example of a potential solution that attempts to partially address the above-listed problems is included in US Patent Publication No. 2003/0222550 (U.S. application Ser. No. 10/417,111 filed Apr. 17, 2003), invented by Boswell et. al and currently assigned to Xyratex Ltd. of Great Britain, which is hereby incorporated by reference for all purposes. However, the Boswell teachings do not fully address many of the relevant issues discussed above.